A fan is an air pump, powered by a motor, which produces a volumetric flow of air at a certain pressure. The rotating portion of the fan, known as an impeller, comprises a hub with radiating blades that converts torque from the motor to increase static pressure across the hub. The increased static pressure increases the kinetic energy of the air particles, causing them to move. Fans are thus useful for air movement and ventilation.
Fans come in many forms. Axial fans include impellers that rotate to move large amounts of air at low pressure. The air moves in a direction parallel to the fan blade axis. Axial fans can produce a high rate of airflow and are inexpensive to produce, but are useful only in low-pressure environments. Further, axial fans are noisy when the ambient conditions are unfavorable, such as when there is insufficient air or when the airflow is blocked, such as in ductwork.
Centrifugal fans, also known,as blowers, also include rotating plates with radially extending blades, but blowers use centrifugal force to move the air. Airflow from the blower tends to be perpendicular to the blade axis, and at a lower flow rate than with axial fans. Centrifugal fans are more expensive to produce than axial fans and can generally operate at about four times the pressure of axial fans.
Although fans come in many varieties, higher-quality fans tend to operate more quietly and more efficiently. A good quality fan may include ball bearings for smoother operation of the impeller, and preferably has a snug fit between the blades and the fan housing, to ensure that leakage does not occur during operation. Care in manufacture, such as guaranteeing that each blade matches in size, weight, and configuration, may also improve fan efficiency.
The amount of airflow delivered by the fan is related to the fan's construction and placement. The number and length of the fan blades are important, as well as the distance of the fan from other objects and the speed of the fan motor. Ultimately, though the fan efficiency is determined by the design and arrangement of the fan blades.
Processor-based systems, such as desktop computers, generate a substantial amount of heat. These systems often include fans for the power supply, the hard disk drive, and one or more heat sinks placed on the heat-producing microprocessor. Surprisingly, little attention is paid to the design of the fan blades for these uses. The limitation in air intake within the processor-based system, as well as the increasing demand for more effective heat sinks makes the design of a fan in such systems of paramount concern.
Thus, there is a need for a fan assembly wherein the volume of air available for intake into the fan as well as the amount expelled from the fan is maximized.